US 7920344 B2
Arrangements for mounting an optical element, such as a lens or a mirror, are disclosed.
1. An arrangement, comprising:
an optical element having an outer peripheral area and at least three constraint locations arranged at the outer peripheral area of the optical element;
a constraining device for each of the constraint locations, at least one of the constraining devices having a carrier body;
elastically resilient elements arranged in the carrier body of the at least one of the constraining devices; and
a support supporting each of the constraining devices,
wherein, in at least one of the constraint locations, the optical element is constrained in two opposite directions through force-based contact with the elastically resilient elements.
2. The arrangement according to
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5. An assembly, comprising:
a plurality of constraining devices attachable to a support, at least one of the constraining devices having a carrier body; and
elastically resilient elements arranged in the carrier body of the at least one of the constraining devices,
wherein the assembly is configured so that an optical element having constraining locations at its outer periphery can be constrained via at least one of the constraint locations in at least three directions through force-based contact with the elastically resilient elements.
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22. A device, comprising:
at least two assemblies according to
This application is a continuation of, and claims priority under 35 U.S.C. §120 to, U.S. patent application Ser. No. 11/959,914, filed Dec. 19, 2007 now abandoned, which is a continuation of, and claims priority under 35 U.S.C. §120 to, international application serial number PCT/EP2006/006353, filed Jun. 30, 2006, which claims the benefit of U.S. patent application Ser. No. 60/696,432, filed Jul. 1, 2005. The above-noted applications are incorporated by reference herein.
The disclosure relates to arrangements for mounting an optical element, such as a lens or a mirror.
Criteria for mounting optical components in supports have been published, for example, in the article “Flexure mounts for high-resolution optical elements” by D. Vukobratovich, Proc. Of SPIE Vol 0959, Optomechanical and Electro-Optical Design of Industrial Systems, ed. R. J. Bieringer, K. G. Harding (January 1988).
In one aspect, the disclosure provides an arrangement that includes an optical element, a constraining device and elastically resilient elements. The optical element has an outer peripheral area and at least three constraint locations arranged at the outer peripheral area of the optical element. The constraining device has a carrier body, and the elastically resilient elements are arranged in the constraining device. The optical element is constrained via the constraint locations in at least one direction through force-based contact with the elastically resilient elements, and the constraining device constrains the optical element in a statically determinate manner in the carrier body.
In another aspect, the disclosure provides a device that includes two arrangements of the type described in the preceding paragraph, where the optical elements of the arrangements are arranged on a single carrier.
In a further aspect, the disclosure provides an assembly that includes a constraining device having a carrier body. The assembly also includes elastically resilient elements arranged in the constraining device. The assembly is configured so that an optical element having constraining locations at its outer periphery can be constrained via the constraint locations in at least one direction through force-based contact with the elastically resilient elements. The constraining device can constrain the optical element in a statically determinate manner in the carrier body.
In some embodiments, the disclosure can provide an improved approach for supporting an optical component, such as a lens.
In certain embodiments, an optical element is constrained in at least one direction by way of constraint areas that are in force-based contact with elastically resilient elements, where the elastically resilient element for each constraint area is located in a constraining device with a carrier body and the constraining devices hold the optical element on the carrier body in a statically determinate manner.
Certain optical elements such as mirrors or lenses which, due to their shape, are sensitive to deformation, a technical concept is proposed for the connection between the optical element which consists of glass or a similar material, and the mount which holds the optical element in at least three places. In view of the kinematic support concept, it can be desirable to use at these three locations two coupling locations, each exerting two holding forces. In this case, either an axial force is used in combination with a tangential force, or an axial force in combination with a force of arbitrary direction in a plane that extends orthogonal to the optical axis, wherein as a principle the lines of action of these forces should not intersect each other in one point. The terms “axial”, “radial” and “tangential” refer to the optical axis of the element and the projection of the outside contour of the optical element into a plane that extends orthogonal to the optical axis.
In some embodiments, time-dependent effects such as settling effects in coupling locations and relaxation of internal stresses between components can largely be avoided. Therefore, the number of contact locations is also limited to a minimum. To hold the elements, a connection can be realized exclusively with force-based contact, and no frictional connections are used. Due to the use of elastic forces of minimal magnitude, the occurrence of distortion-causing stresses can be reduced to a minimum.
According to the concept of the disclosure, connections with force-based contact are used instead of connections with frictional contact. Some advantages of this kind of a connection are described in the following.
With a movement, more specifically an acceleration A, of the optical element of the mass M for example in an x-direction which may represent a tangential direction, for example as a result of a shock load, a change in force FT=M×A will act on the optical element in the tangential direction (or generally in the direction of the acceleration), which in a friction-based holder arrangement (for example via a leaf spring or a diaphragm spring) of the optical element would involve holding forces of a magnitude of at least FRS=M×A/μ. In a holder arrangement with force-based contact via a soft spring, optionally having a flat spring characteristic, a change in force of an amount of only ΔFKS=M×A is applied to the optical element in order to hold it in position. The force FRS in this example is acting perpendicular to the seating surface of the optical element so that in case of an axial acceleration of the optical element, this force will act in the axial direction (Faxial). The symbol μ stands for the coefficient of static friction which, with the desired precise finish of the seating surfaces, is in the range from about 0.1 to 0.2. Due to the small coefficient of static friction, a significantly larger axial force Faxial is needed for example in case of an acceleration in the x-direction in order to hold the optical element than would be the case with a holder arrangement of the optical element with force-based contact, where the inertial forces of acceleration are absorbed directly for example via elastic elements. As the foregoing example shows, the amount of ΔFKS to hold the element through force-based contact is very much smaller than the amount for FRS desired for holding the element through friction-based contact, so that in the former case the optical element is exposed to a lower overall level of mechanical stress. In the case of a connection by force-based contact through an elastic device, the spring force, i.e. the force generated by the deformation of the elastic device acting against the direction of the acceleration, will push the optical element back to its original position, while in the case of a friction-based connection the optical element can behave in a non-defined way, if for example its fixation through static friction is compromised for short time intervals. It further needs to be pointed out that with a friction-based holding arrangement of the optical element, the large force effecting the friction hold needs to act on the optical element continuously, while with a holding arrangement of the optical element that is based on force-based contact, the optical element is exposed to a force that depends on the elastic properties of the elastic elements providing the force-based connection and is significantly reduced in comparison to the friction based connection, and this reduced force is present only at the occurrence of the aforementioned acceleration A of the optical element or in case of an abrupt force acting on the optical element (see description of
With a connection based purely on frictional contact, to ensure that the optical element remains in its original position, the force acting on the optical element as a result of a force pulse should not exceed the static friction force. Thus, if under a force pulse the same force ΔFKS takes effect as in the force-based contact connection discussed above, the optical element will not change its position, i.e. stay securely in place, if the multiplication product of the static friction coefficient μ and a force FRS which is acting perpendicular to the surfaces providing the static friction between the optical element and the holder element is larger than the force ΔFKS caused by the force pulse, i.e. if FRS×μ>ΔFKS. This is based on the assumption that the force caused by the force pulse has the direction of the surfaces which provide the static friction. If this is not the case, then ΔFKS needs to be replaced by the force component in the direction, which can be obtained by representing ΔFKS through a set of vector components. If the condition FRS×μ>ΔFKS is not met, there is a risk that the optical element becomes displaced from its original position and takes on a new position in which it remains even after the force has subsided, i.e. after the shock has ended.
As described above, because of the small value of the coefficient μ of static friction, the force FRS in a friction-based holding arrangement of the optical element needs to be about 5 to 10 times as large as the maximum amount of the forces that have to be anticipated as a result of force pulses acting on the optical element or as a result of accelerations of the optical element. This is indicated schematically in
In some embodiments, protrusions are formed on the optical element. Advantageously, the protrusions are formed out of the optical element itself. As an alternative, they can also be formed by elements such as ledges, consoles or small blocks that are attached to the optical element for example by wringing or by adhesive bonding.
It further turns out to be advantageous if two coupling locations are provided at each of the protrusions which are acted on by two holding forces serving to hold the optical element in the carrier body.
Advantageously, in an arrangement of this kind an axial force as well as a tangential force act on the optical element at each of the coupling locations.
As an alternative to this concept, it can also be advantageously envisioned that at each of the coupling locations an axial force and a further force oriented in an arbitrary direction perpendicular to the axis of the optical element are acting on the optical element, wherein the arbitrarily directed forces have lines of action that are not intersecting each other in a single point.
An arrangement is advantageous in which the protrusions are held exclusively by force-based contact.
According to the disclosure, by using elastic forces of a minimal magnitude to hold the optical element, the distortion-causing stress of the optical element can be reduced to a minimum.
An arrangement is of advantage in which the elastic elements are arranged in holder devices which partially surround the elastic elements.
Advantageously, the elastic elements are constituted by pre-tensioned compression springs.
It is envisioned in a further advantageous embodiment that the compression springs are holding the protrusions in the axial and tangential directions. This arrangement can be realized advantageously with one or two compression springs arranged in the tangential direction and one or two compression springs arranged in the axial direction.
It is advantageous if the compression springs are pre-tensioned only far enough to enable them to absorb shock loads occurring during transportation of the optical element.
In a further advantageous embodiment of the inventive arrangement, it is envisioned that the compression springs are arranged in a clamping unit which receives the carrier body and holds the latter by way of a monolithically formed hinge.
In addition the monolithic hinge can be realized advantageously as a bipod via two rods.
It can be advantageous if the protrusions of the optical element or the optical element itself, such as its border area, contains notches or grooves in the axial direction, optionally in the radial and/or tangential directions for the connection with elastically resilient elements of the constraining device.
It can be advantageous if the compression springs are received by the notches or grooves. There can also be spacer elements inserted between the compression springs and the, e.g., V-shaped grooves or depressions.
In a further embodiment of the disclosure, the protrusions of the optical element are held by way of the elastic elements, specifically by way of the compression springs, in a clamp that belongs to the constraining device.
The use of compression springs exerting a reduced force (in contrast to arrangements in which the optical element is clamped through friction based contact) reduces displacements and deformations of the coupling locations caused by clamping forces and also reduces relaxation- and settling effects if an appropriately small spring constant is chosen for the springs (see
The kinematic uncoupling by way of monolithic hinges reduces the number of contact locations and leads to a support arrangement that can be optimized statically and dynamically through known methods. By way of the attachment of three bipods at the outer support ring or also by the integration in the bipods themselves, an active adjustment can be achieved by way of piezoelectric of an electromagnetic drive device.
The disclosure also relates to a device that comprises two arrangements, each of which includes an optical element, wherein each of the optical elements is of a design as described above. The optical elements are arranged in this device with clamping elements or constraining devices that are arranged in alternatingly standing and hanging positions on a single support ring.
The disclosure is explained in more detail below with references to the drawing, wherein:
A clamping element 1 (see
Installed in the cutout 3 and connected to the carrier body 2 by way of holder plates 8, 9, 10 (
Besides the clamping element (constraining device) 1, the lens 18 is held by two further constraining devices (clamping elements) 19, 20, wherein in each of the constraining devices the pre-tensioned compression springs 14, 15, 16 hold the lens 18 by the protrusion which is placed in between the springs.
On a protrusion 23 (see
In an embodiment according to
For force pulsed in the tangential direction, whose force components are oriented in the direction from the cylindrical pin 30 towards the spring 26, the spring 26 and the cylindrical pin 30 perform an analogous function as the springs 24 and 25 and the rigid elements 27 and 28. The spring 26 can likewise be pre-tensioned, optionally with the amount of pre-tension being selected so that it approximately matches the maximum amount of force that occurs under the anticipated force pulses. This prevents that the protrusion is separated or lifted off from the contact surface at the cylindrical pin 30. Analogous to the springs 24 and 25, the amount of pre-tension of the spring 26 can be selected smaller than the expected maximum force from a force pulse, in which case the protrusion 17 can momentarily lift off from the contact surface of the cylindrical pin 30. Subsequently, as the force subsides, the protrusion is brought back into contact with the cylindrical pin 30 via the spring 26. Thus, after a force pulse with a tangential force component (for example due to a jolt or shock) the optical element returns to the desired position which is defined by the cylindrical pin 30. The springs shown in
In another embodiment which is illustrated in
In a further embodiment which is illustrated in
In a further embodiment of the disclosure which is illustrated in
Other embodiments are in the claims.